Omnidirectional rotational speed and rotational direction sensor

Abstract

The present invention relates to a magnetic field sensor (1) which is designed to determine the rotational speed and rotational direction of a rotating object (20) which either generates a rotating magnetic field itself or deflects an existing magnetic field accordingly. For this purpose, a chip (2) having at least three magnetic field measuring elements (2a, 2b, 2c) in the form of a 3D Hall sensor is used. Such magnetic field sensors (1) are used in particular in commercial vehicles. A normal direction in relation to the tangential plane of the rotating element defines a z-direction. A differential signal is formed from the signal from a sensor element having a sensitivity in the z-direction together with the signal from a further sensor element. The two resulting differential signals have a phase shift from which the rotational direction can be determined. A generated output signal contains information about both the rotational direction and the speed.

Description

[0001] The present invention relates to an omnidirectional speed and direction sensor, particularly for use in commercial vehicles, for example trucks.

[0002] Autonomous driving, in particular, requires speed sensors that determine the speeds and directions of rotation of specific components, such as shafts, gears, or individual wheels in a commercial vehicle. It is particularly important that both the speed (i.e., the rotational speed) and the direction of rotation are measured.

[0003] In the prior art, so-called passive sensors are known for this purpose. These are fixedly mounted near a rotating object, such as a shaft or a gear. Due to the technology, the radial orientation of the sensor is not important for passive sensors.

[0004] Active sensors already exist in passenger cars where the radial orientation of the sensor is important. Here, the sensor is fixed in position or firmly screwed in place, so that the exact direction and speed of rotation of a shaft or rotating part can always be determined.

[0005] However, in commercial vehicles, such active sensors require axial displacement due to specific requirements. A sensor must therefore be movable and always deliver the same measurement result, regardless of its position relative to the rotating object.

[0006] Known in the prior art is, for example, patent document EP 3 304 003 B1, which discloses a magnetic field sensor for performing independent speed and direction measurement.

[0007] Here, the sensor contains a first, a second and a third spaced apart magnetic field measuring element, each of which outputs a magnetic field signal proportional to the

[0008] Amplitude of a magnetic field associated with a rotating object. Pairs of differences between all three measured values ​​are determined, and corresponding difference signals are generated, which are output as differential channels. A combiner generates a combined signal based on the first, second, and third magnetic field signals. A control circuit then calculates the rotational speed and determines the direction of rotation, generating a sensor output signal indicating the speed and direction of movement of the rotating object.

[0009] This sensor can be provided regardless of the location of the rotating object.

[0010] Hall sensors are used in particular here, which measure the magnetic field emanating from a rotating object at three points, and from this the control unit can calculate a speed and a direction of movement.

[0011] However, calculating three difference channels is complex, consumes computing time and requires memory space.

[0012] Furthermore, document US 2012 / 249133 A1 is known from the prior art. This document discloses a differential magnetic field sensor that enables operation independent of the sensor-to-target orientation. The differential magnetic field sensor is equipped with at least two differential channels. Each differential channel contains a pair of magnetic field sensor elements and has a corresponding sensor axis defined by these magnetic field sensor elements. The detection axes are not aligned with each other.

[0013] Furthermore, the document US 2017 / 322233 A1 is known from the prior art. This discloses a magnetic sensor comprising a first sensor element and a second sensor element. The first sensor element may be capable of detecting a first component of a magnetic field that is not parallel to an axis formed by an intersection of a first plane and a second plane. The first plane may be a plane in which a gear rotates, and the second plane may include a first surface of the first sensor element and a second surface of the second sensor element. The first component of the magnetic field may lie in the second plane. The second sensor element may be capable of detecting a second component of the magnetic field. The second component of the magnetic field may lie in the second plane.

[0014] It is therefore the object of the present invention to provide an improved magnetic field sensor for determining a direction of rotation and a speed of a rotating object, in which the computing time can be reduced and the accuracy can be increased.

[0015] This object is achieved by a system comprising a magnetic field sensor and a pole wheel according to claim 1 and by a method according to claim 9.

[0016] Further advantageous embodiments are the subject of the dependent claims.

[0017] An inventive system comprising a magnetic field sensor and a pole wheel comprises: a pole wheel with teeth and gaps, the pole wheel being magnetically encoded or magnetically biased; a magnetic field sensor comprising: a chip with at least a first, a second, and a third magnetic field measuring element, each adapted to provide a first, a second, and a third magnetic field signal, the amplitudes of which are proportional to a magnetic field emanating from a rotating object (or emanating from a permanent magnet and deflected by the movement of the rotating object). The normal vectors of the at least three magnetic field measuring elements are linearly independent of each other. This means that they can, for example, each enclose an angle of 90° with each other, such as a Cartesian coordinate system.A signal acquisition unit is adapted to determine a first difference signal and a second difference signal, wherein the first difference signal is based on a difference between the magnetic field signal of the first magnetic field measuring element and the second magnetic field measuring element, and the second difference signal is based on a difference between the magnetic field signals of the first magnetic field measuring element and the third magnetic field measuring element. The signal acquisition unit is further adapted to calculate and output a combined signal based on the magnetic field signal of the first magnetic field measuring element as well as the first difference signal and the second difference signal. An evaluation unit is then adapted to generate an output signal which, based on the combined signal, includes a movement speed and a movement direction of the pole wheel.

[0018] The at least three magnetic field measuring elements are Hall sensors. Such sensors are relatively inexpensive compared to other sensors, yet still very accurate.

[0019] Hall sensors consist of doped semiconductor layers that have, for example, four electrodes on their sides. A current is fed through two opposite electrodes, and the so-called Hall voltage is then applied to the two orthogonal electrodes. When a magnetic field perpendicular to the layer flows through a Hall sensor, it produces an output voltage proportional to the vector product of the magnetic flux density and the current. The cause of this Hall voltage is a Lorentz force acting on the moving charge carriers in the doped semiconductor layer.

[0020] The first magnetic field element is a lateral Hall sensor, and the second and third magnetic field measuring elements are each vertical Hall sensors. The vertical Hall sensors are positioned parallel to the magnetic flux lines and extend parallel to the plane of the chip. In contrast, the vertical Hall sensors are perpendicular to the magnetic flux lines and are also perpendicular to the chip.

[0021] The first magnetic field measuring element is a lateral Hall sensor and is mounted flat on the chip, and the second and third magnetic field measuring elements are each vertical Hall sensors, which stand with their small surface on the chip and are thus arranged perpendicular to the chip,

[0022] This, in turn, has the advantage that, thanks to the lateral Hall sensor, a change in magnetic flux is independent of the arrangement—meaning a magnetic field can always be measured. The magnetic field sensor could therefore also be moved away from the rotating object and still measure with sufficient accuracy.

[0023] The magnetic field sensor in this case is a 3D Hall sensor, and it works with two differential signals because the change in magnetic flux in one direction is independent of the arrangement - because a Hall voltage is always generated regardless of the direction of rotation and rotational speed. Direction detection here is basically carried out via the phase shift, i.e. the difference between the minima and maxima of the amplitudes of the individual magnetic field measuring elements. Two differential signals are therefore sufficient for direction detection. A magnetic flux signal can also provide further diagnostic options, for example, determining the thickness of the air gap between the magnetic field sensor and the rotating object. If this happens in a commercial vehicle, an increasing air gap could, for example, indicate that the position of the magnetic field sensor relative to the rotating object has changed over time and the driver therefore needs to visit the workshop.

[0024] Further preferably, a vectorial evaluation can be carried out.

[0025] Preferably, the normal vectors of the three magnetic field measuring elements each enclose an angle of approximately 90°, preferably exactly 90°, with each other. Such an arrangement allows the maximum amplitude of all signals to be measured.

[0026] Even more preferably, further magnetic field measuring elements are provided, which are arranged, for example, at a 45° angle between the three magnetic field measuring elements, which enclose an angle of 90° with each other.

[0027] The chip is arranged in a plane that is largely parallel, preferably parallel, to a tangential plane of the rotating object. This, in turn, ensures that one of the measurement signals is independent of the orientation, and that an accurate measurement is possible even as the gap between the rotating object and the chip increases.

[0028] Further preferably, the chip and the at least three magnetic field elements are housed in a housing, and the chip can preferably be secured with a holder. The holder ensures that the chip with the magnetic field measuring elements is firmly fixed in the housing and thus stationary. Thus, it is sufficient to calibrate the magnetic field sensor once, and it can then remain in use without the need for repeated recalibration.

[0029] The interior of the housing is preferably at least partially filled with a plastic material. This increases the stability of the position of the magnetic field sensor within the housing.

[0030] Furthermore, flux guide plates are preferably provided on the housing in order to minimize interference signals in the area of ​​the chip.

[0031] Further preferably, the magnetic field sensor further comprises a current or voltage interface with which signals can be output, for example to a control system of a commercial vehicle.

[0032] Further preferably, the evaluation unit of the magnetic field sensor is configured to perform temperature compensation of the measurement signals of the at least three magnetic field measuring elements.

[0033] Thus, a sufficiently accurate signal is obtained at different temperatures, and the temperature dependence of rotational speed and rpm or the measurement error can be minimized.

[0034] A system according to the invention consists of a magnetic field sensor and a pole wheel, whereby the pole wheel can be magnetically coded or magnetically preloaded.

[0035] Magnetically coded can mean that small permanent magnets are arranged on the teeth of the pole wheel, each of which generates a magnetic field.

[0036] Magnetically biased means that the pole wheel is made of a ferritic material, and by providing a permanent magnet on the chip of the magnetic field sensor, the magnetic field excited by the permanent magnet is deflected depending on the rotation of the pole wheel - the magnetic field lines then run into one or more teeth of the pole wheel, but not into the gaps, and are then deflected by the rotation of the pole wheel.

[0037] The magnetic field of the pole wheel, together with the magnetic field emanating from the magnet on the chip, generates a magnetic signal, which can then be measured by the magnetic field sensor.

[0038] Further preferably, the system includes a further differential element, for example, an optical sensor, which is further adapted to determine the direction of rotation of the rotor. This enables even more precise and reliable measurement.

[0039] A further differential element can also be adapted to detect and / or compensate for external fields.

[0040] A method according to the invention for determining a speed and a direction of rotation of a rotating object using a system according to the invention comprises the following steps: a) Detecting a magnetic field signal from each of the first magnetic field measuring element, the second magnetic field measuring element, and the third magnetic field measuring element; b) Determining a first difference signal from a difference between the magnetic field signals of the first magnetic field measuring element and the second magnetic field measuring element; c) Determining a second difference signal from a difference between the magnetic field signals of the first magnetic field measuring element and the third magnetic field measuring element; d) Calculating a combined signal from the magnetic field signal of the first magnetic field measuring element, the first difference signal, and the second difference signal; e) Calculating and outputting an output signal containing a movement speed and a movement direction of the rotating object.

[0041] In the following, a preferred embodiment of the present invention is described with reference to the accompanying figures.

[0042] Fig. 1 shows a plan view and a schematic view of a magnetic field sensor 1 according to the invention and a pole wheel 20 in three different orientations ( Fig. 1 a) bis 1 c )).

[0043] In Fig. 2 are typical magnetic field signals of the individual magnetic field elements in each of the three orientations Fig. 1 shown, where the course of the magnetic field signals is recorded over time, i.e. when the pole wheel rotates ( Fig. 2 a) bis 2 c )).

[0044] In Fig. 3 an arrangement of a magnetic field sensor according to the invention in a housing is shown.

[0045] In Fig. 1 1 shows the magnetic field sensor 1 according to the invention and a magnet wheel 20. The magnetic field sensor 1 is shown in plan view and arranged above the magnet wheel 20. The magnet wheel 20 has teeth 21 and gaps 22. The magnetic field sensor includes a chip 2, on which three magnetic field measuring elements 2a, 2b, and 2c are arranged. Furthermore, the magnet 2d is arranged on this chip. The magnetic field measuring elements 2a, 2b, and 2c are basically cuboid-shaped, with a larger base area and small, narrow side surfaces. The first magnetic field measuring element 2a, as a lateral Hall element, is mounted flat on the chip 2 and rests with its large base area on the chip 2. Here, a Hall voltage can always be measured when the magnet wheel 20 rotates. The other two magnetic field measuring elements 2b and 2c are vertical magnetic field measuring elements and stand with their small surface on the chip and are thus arranged perpendicular to the chip.The chip 2 is parallel to a tangential plane of the pole wheel 20. In . Fig. 1 b) Chip 2 is off Fig. 1a rotated by 45°, so the position of the magnetic field measuring elements 2a, 2b, and 2c has also changed. Despite this, the chip 2 still lies in a plane parallel to a tangential plane of the pole wheel 20. Fig. 1 c) This representation is rotated again by 45°, here too the chip 2 lies in a plane which is parallel to the tangential plane of the pole wheel 20.

[0046] In Fig. 2 the course of the magnetic field strengths, i.e. the signal of the sensors 2a, 2b and 2c, is shown over time (or in this case: depending on the angle of rotation) and depending on the orientation of the chip 2. Fig. 2a ) corresponds to the representation in Fig. 1 a)

[0047] The signal of the second magnetic field measuring element 2b (in Fig. 2 drawn as Bx) has a significantly lower amplitude than the signals of the first magnetic field measuring element 2a (in Fig. 2 referred to as Bz) and the third magnetic field measuring element 2c (in Fig. 2 referred to as By), since here the magnetic lines of the magnet 2d, which are deflected by the pole wheel 20, can only cause a Hall voltage in the second magnetic field measuring element 2b (since the magnetic field lines are not perpendicular to the direction of extension of the second magnetic field measuring element 2b). The signals of the first and third magnetic field measuring elements 2a and 2c have a larger amplitude, since here the magnetic field lines run perpendicular to the respective Hall element and can therefore cause stronger Hall voltages. The two amplitudes of the magnetic field measuring elements 2a and 2c are phase-shifted, which can be explained by the fact that the magnetic field change at these two elements occurs at a different time, since they are spaced from one another in the direction of rotation of the pole wheel 20 and thus the teeth 21 of the pole wheel pass the chip 2 with a different time delay - and thus the deflection of the magnetic field lines of the permanent magnet 2d occurs with a different phase delay.

[0048] In Fig. 2 b) It is illustrated that the signals of the magnetic field measuring element 2b and 2c have a similar shape, since here in each case components of the magnetic field acting by the permanent magnet 2d, which is deflected by the rotation of the pole wheel 20, act, which are correspondingly perpendicular to the Hall elements and can thus cause a Hall voltage.

[0049] In Fig. 2 c) The measuring signals of the sensors in the arrangement are Fig. 1 c) shown. Strong fluctuations in the signals from the first and second magnetic field measuring elements 2a and 2b are shown here, each phase-shifted. This can be explained by the spatial separation of the first and second magnetic field measuring elements 2a and 2b in the direction of rotation. However, slight fluctuations can be seen from the third magnetic field measuring element 2c, since only a very small proportion of the magnetic field lines enter perpendicular to the Hall sensor, and thus, no strong Hall voltage can be generated in the direction of extension of the third magnetic field measuring element 2c.

[0050] These signals can be used to determine both the rotational speed and the direction of rotation. The phase shift, in particular, allows for the detection of the direction of rotation. Two channels are sufficient for direction detection; three channels are not required. This saves computing time, allowing the results of the calculations for the direction of rotation and the rotational speed to be provided more quickly.

[0051] In Fig. 3 An arrangement of the chip 2 in a housing 5 is shown. The chip 2 is attached to the housing 5 with a holder 6. The interior of the housing 5 is partially filled with a plastic material. This better secures the chip in the housing. The position of the housing relative to a magnet wheel is also shown. The air gap L between magnet wheel 20, which has teeth 21 and gaps 22, and the housing 5 can vary accordingly. Furthermore, it is indicated that the signal acquisition unit 3, evaluation unit 4, and the current or voltage interface 7 are located on the chip.

[0052] In the area of ​​the chip 2, a flux guide plate 8 is also shown, which is intended to keep magnetic interference fields away from the chip 2.

[0053] The present invention is not limited to the described embodiment. It is important that at least three Hall elements are present, whose normal vectors are linearly independent of each other. However, additional elements can be arranged between them, for example, additional Hall elements at a 45° angle to the corresponding measuring elements 2a, 2b, and 2c. This would further increase accuracy.

[0054] The present invention relates to a magnetic field sensor 1 adapted to determine the movement of a rotating object 20, which either generates a rotating magnetic field itself or deflects an existing magnetic field accordingly, in particular the direction of rotation and speed of the rotating object. For this purpose, a chip 2 with at least three magnetic field measuring elements 2a, 2b, 2c is used, preferably a 3D Hall sensor. Such magnetic field sensors 1 are used particularly in commercial vehicles. Bezugszeichenliste

[0055] 1Magnetic field sensor 2Chip 2aFirst magnetic field measuring element 2bSecond magnetic field measuring element 2cThird magnetic field measuring element 2dPermanent magnet 3Signal acquisition unit 4Evaluation unit 5Housing 6Holder 7Current or voltage interface 8Flux guide plate 20Pole wheel 21Tooth 22Gap D1First differential signal D2Second differential signal KSCombined signal ASOutput signal

Claims

1. System comprising a magnetic field sensor (1) and a pole wheel (20) with teeth (21) and gaps (22), wherein the pole wheel (20) is magnetically coded or magnetically pre-stressed, wherein the magnetic field sensor (1) comprises: a chip (2) having at least a first, a second and a third magnetic field measuring element (2a, 2b, 2c), which are each configured to output a first, second and third magnetic field signal (S1, S2, S3), the amplitudes of which are proportional to a magnetic field emanating from the pole wheel (20), wherein the directions of the normal vectors of the at least three magnetic field measuring elements (2a, 2b, 2c) are linearly independent of one another, a signal acquisition unit (3), which is configured to determine a first differential signal (D1) and a second differential signal (D2), wherein the first differential signal (D1) is based on a difference between the magnetic field signals of the first magnetic field measuring element (2a) and the second magnetic field measuring element (2b), and the second differential signal (D2) is based on a difference between the magnetic field signals of the first magnetic field measuring element (2a) and the third magnetic field measuring element (2c), and the signal acquisition unit (3) is further configured to determine a combined signal (KS) from the magnetic field signal of the first magnetic field measuring element (2a) as well as the first differential signal (D1) and the second differential signal (D2), an evaluation unit (4), which is configured to generate an output signal (AS), which, based on the combined signal (KS), contains a speed of motion and a direction of motion of the pole wheel (20), wherein the first magnetic field measuring element (2a) is a lateral Hall sensor and is mounted flat on the chip (2), and the second and third magnetic field measuring elements (2b, 2c) are each vertical Hall sensors, which stand on the chip (2) with their small surface and are thus arranged perpendicular to the chip (2), wherein the chip (2) is arranged in a plane which is substantially parallel to a tangential plane of the pole wheel (20).

2. System according to claim 1, wherein the normal vectors of the three magnetic field measuring elements (2a, 2b, 2c) each include an angle of 90° to one another, and optionally further magnetic field measuring elements are provided.

3. System according to any one of the preceding claims, wherein the chip (2) with the at least three magnetic field measuring elements (2a, 2b, 2c) is housed in a housing (5), and the chip (2) is preferably fastenable with a holder (6), wherein the interior of the housing (5) is further preferably at least partially filled with a plastics material, and preferably flux guide plates (8) are provided to minimize interference signals in the region of the chip (2).

4. System according to any one of the preceding claims, wherein the magnetic field sensor (1) has a current or voltage interface (7).

5. System according to any one of the preceding claims, wherein the evaluation unit (4) is configured to perform a temperature compensation of the measurement signals of the at least three magnetic field measuring elements (2a, 2b, 2c).

6. System according to any one of the preceding claims, wherein the chip (2) of the magnetic field sensor (1) is magnetically pre-stressed, preferably by providing a permanent magnet (2d) on the chip (2).

7. System according to any one of the preceding claims, wherein a further differential element (8) is also provided, which is configured to determine the rotational direction of the pole wheel (20).

8. System according to any one of the preceding claims, wherein a further differential element (8) is also provided, which is configured to determine and / or compensate for extraneous fields.

9. Method for determining a rotational speed and a rotational direction of a pole wheel (20) using a system according to any one of claims 1 to 8, comprising the following steps: a) detecting one magnetic field signal (S1, S2, S3) each from the first magnetic field measuring element (2a), the second magnetic field measuring element (2b), and the third magnetic field measuring element (2c); b) determining a first differential signal (D1) from a difference between the magnetic field signals (S1, S2) of the first magnetic field measuring element (2a) and the second magnetic field measuring element (2b); c) determining a second differential signal (D2) from a difference between the magnetic field signals (S1, S3) of the first magnetic field measuring element (2a) and the third magnetic field measuring element (2c); d) calculating a combined signal (KS) from the magnetic field signal (S1) of the first magnetic field measuring element (2a) as well as the first differential signal (D1) and the second differential signal (D2); e) calculating and outputting an output signal (AS), which contains a speed of motion and a direction of motion of the pole wheel (20).

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